1. Field of the Invention
The present invention relates to a semiconductor element and a manufacturing method thereof, and more specifically, to a semiconductor element which chiefly serving as an "anti fuse" and a manufacturing method thereof, the anti fuse storing data by causing a transition from a high resistance state to a low resistance state by a current supplied when a voltage is imposed.
2. Description of the Related Arts
An anti fuse operates such that when a voltage is imposed to an electrode of a semiconductor element and a current is supplied thereto, the current causes the electrode to change from a nonconductive state to a conductive state. More specifically, the anti fuse forms a semiconductor element which has a characteristic and function opposite to those of a "fuse", wherein, for example, a conductive state is conventionally changed to a nonconductive, state by breaking a wiring of polysilicon.
Conventionally, chalcogenide and amorphous silicon are known as materials used for the anti fuse, and examples of their practical applications are shown in the following documents. The feature of the anti fuse shown in these documents will be described below.
Document 1: Japanese Examined Patent Publication No 47-32944/72
The energy applied to a high resistance semiconductor material composed of amorphous silicon by irradiating an electron beam, a laser beam and the like cases a stable high resistance state of the semiconductor to change to a stable low resistance state.
Document 2: Japanese Examined Patent Publication No. 57-4038/82
A PROM device composed of high resistance polysilicon of which the resistance value is unreversibly changed by an imposed electric field.
Document 3: Japanese Laid Open Application No. 54-88739/79
An EEPROM device composed of tellurium-based chalcogenide having a high electric resistance in an amorphous state and a low electric resistance in a crystallized state.
This anti fuse is applied to a simple wiring connection switch in an IC, a PLA (programmable logic array) and a redundant circuit of a memory, and further to a PROM, and its application to these devices is under consideration.
FIG. 2 is a schematic partly cross-sectional view of a conventional semiconductor element used as the above anti fuse and of a type most closely related to the semiconductor element of the present invention.
In FIG. 2, 201 designates a semiconductor substrate, 202 designates an impurity diffusion layer formed on the surface the semiconductor substrate 201, 203 and 203a designated an inter-layer insulation film, 204 designates a wiring electrode, 205 designates an amorphous silicon region, and 206 designates an upper electrode formed on the amorphous silicon 205. Note, the amorphous silicon 205 is a high resistance member.
The upper electrode 206 is composed of a conductive material and is formed simultaneously when the wiring electrode 204 is formed.
In this arrangement, the wiring electrode 204 and the amorphous silicon 205 are formed substantially in contact with the opposite ends of the impurity diffusion layer 202 and the amorphous silicon 205 is inserted between the upper electrode 206 and a lower electrode composed of the impurity diffusion layer 202, wherein the amorphous silicon of high resistance serves as a chief constitutional portion of the above anti fuse. More specifically, when a voltage is imposed between the upper electrode 206 and the wiring electrode 204 coupled with the lower electrode 202 to supply a current, an unreversible transition from a high resistance state to a lower resistance state is caused in the amorphous silicon 205 between both the electrodes. That is, a memory element can be composed by making use of the fact that a portion of the amorphous silicon 205 is changed from a nonconductive state to a conductive state.
The conventional semiconductor element arranged as described above is preferably provided with a higher resistance value before transition, R.sub.off, and a lower resistance value, R.sub.on, after transition from the view point of the performance of the element. While the amorphous silicon is not preferable because the resistance value before transition, R.sub.off, thereof is a little lower than that of an insulation film composed of an oxide film, it is more reliable than an element using a breakage in an insulation film, and thus it has both advantages and disadvantages. Further, the conventional element is not preferably arranged, because the R.sub.off is considerably lowered in the state before transition although it is effective that acceptor ions, donor ions or the like are added to the amorphous silicon to lower the resistance value after transition, R.sub.on.